The present invention relates to an insole construction that includes a rigid molded shell that is positioned under the heel of a user and extends forwardly to a region adjacent, but rearwardly of the metatarsal heads of the foot. In the preferred form the insole comprises a full foot foam layer above the shell with a covering that includes low friction surface material in selected areas where calluses and blisters are likely to be formed.
In the prior art, various constructions for insoles have been advanced to reduce trauma to a foot and to control shear and stress between the foot and the surface of the insole.
U.S. Pat. No. 4,510,700 shows an adjustable shoe insert that includes a relatively rigid shell that is under the foot and in contact with the footbed of a shoe, and is covered with a foam layer. The shell is positioned at the heel of the foot and has a flange that extends around the heel. Providing force distribution and force dissipation throughout the bone structure of the foot is an objective. However, the configuration does not provide sufficient rigidity to adequately spread shock forces that occur in the feet of runners at the moment of initial contact (heel strike).
U.S. Pat. No. 5,586,398 shows an article of footwear that is for efficient running, and it teaches that controlling friction in a running shoe helps to reduce soft tissue trauma upon foot impact.
These structures are typically shown to be useful for their purposes, but the need exists for a light, comfortable, force distributing insole that adequately manages both shock and friction forces seen by the foot to avoid bruising, blisters, thick calluses and the like.